Most likely, you're getting oil-fouled spark plugs that are causing the performance issues. Once the oil gets into the intake, it's got to go somewhere- - - -into the cylinders, maybe? The only thing in the way of all that oil splashing around in the crankcase (thrown off the crankshaft and rods) is a little piece of sheet metal under the draft tube hole. Chevy wouldn't have gone to all the trouble and expense to make and install that standpipe if it was not needed to control oil splash. Ditto for the road draft tube- - - - -it is placed at the top of a tall, baffled tube- - - - -I wonder why?
LOL!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!